Plasma arc torches are widely used in the cutting and marking of materials. A plasma torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). The torch produces a plasma arc, a constricted ionized jet of a gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen) or reactive (e.g., oxygen or air). During operation, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode). Generation of the pilot arc can be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or by means of any of a variety of contact starting methods.
In plasma cutting systems, the gas flow needed for plasma cutting can be different from the gas flow that is needed for arc ignition. At ignition the gas swirl strength may need to be increased or decreased to provide a stable arc with low erosion, but during cutting the optimum flow rate and swirl strength are often different. Known plasma cutting systems do not permit both the gas chemistry and the gas flow pattern to be optimized independently of each other between and/or during arc ignition, cutting and arc extinction. Optimizing one parameter often requires compromising with respect to another and can cause electrode life to decrease as a result.